Spacecraft motion estimation using a gimballed momentum wheel

Abstract

A method for estimating motion of a dual-spin spacecraft having a gimballed momentum wheel. The method disengages the gimbal from its drive train in anticipation of a short disturbance. Then, the gimbal slip resulting from the disturbance is measured. The method may be used to stabilize any dual-spin spacecraft that uses a gimballed momentum wheel. To stabilize the dual-spin spacecraft, the gimbal angle and gimbal rate are measured during and after the disturbance to provide an indication of the inertial spacecraft motion along gimbal axes. The magnitude and direction of the disturbance are determined by comparing motion of the gimbal before and after the disturbance. Then, torques are applied to the gimbal to counteract the spacecraft motion resulting from the disturbance. Temporarily reducing torque on the gimbal may be accomplished by disengaging the gimbal drive train, disengaging a holding mechanism between motor stator and rotor, or disabling command and back-emf torques, whether the drive is a DC motor or a stepper motor.

What is claimed is:  
     
       1. A method for estimating the motion of a dual-spin spacecraft comprising a momentum wheel attached to a gimbal, said method comprising the steps of: 
       temporarily reducing torque on the gimbal in anticipation of a short disturbance; and  
       measuring gimbal slip resulting from the disturbance.  
     
     
       2. The method of  claim 1  further comprising the steps of: 
       measuring gimbal angle and gimbal rate during and after the short disturbance to provide an indication of the inertial spacecraft motion along gimbal axes;  
       determining the magnitude and direction of the disturbance by comparing motion of the spacecraft before and after the disturbance; and  
       applying torques to the gimbal to counteract the motion of the spacecraft resulting from the short disturbance so as to stabilize the motion of the spacecraft.  
     
     
       3. The method of  claim 1  wherein the step of temporarily reducing torque on the gimbal comprises disengaging the gimbal from the drive train in anticipation of the short disturbance. 
     
     
       4. The method of  claim 1  wherein the step of temporarily reducing torque on the gimbal comprises disengaging a holding mechanism disposed between a motor stator and rotor. 
     
     
       5. The method of  claim 1  wherein the step of temporarily reducing torque on the gimbal comprises disabling command and back-emf torques applied to the gimbal. 
     
     
       6. The method of  claim 1  wherein the step of measuring gimbal slip comprises disengaging the gimbal from the drive train in anticipation of the short disturbance. 
     
     
       7. The method of  claim 1  wherein the step of measuring gimbal slip comprises disengaging a holding mechanism disposed between a motor stator and rotor. 
     
     
       8. The method of  claim 1  wherein the step of measuring gimbal slip comprises disabling command and back-emf torques applied to the gimbal.